This invention relates to a method for the filtration of a suspension by a granular filtrating layer, and an apparatus for practicing the method, of the type for the continuous filtration of sand, usable for the treatment of waters of all nature for the filtration of suspensions or emulsions.
A filter with a granular filtrating layer becomes dirty after a certain period of operation and requires regeneration of the filtrating mass. It is known that, in order to avoid interruption of the filtering of the fluid to be filtrated during regeneration of the filtrating mass and therefore to ensure a continuous operation of the filter, to circulate and clean the filtrating mass while maintaining constant the flow rate of the fluid to be filtered.
Several apparatus have already been described for practicing this atype of method. The filtration is carried out with a current flowing upwardly through a granular mass of sand, and the dirty sand is extracted in a countercurrent direction by using an air or water ejector, also taking part in the regeneration operation.
The recovery of the sand is usually continuous. In some methods, washing of the sand is effected outside the filter. Portions of the sand are extracted, regenerated and recycled without interruption of the operation of the filter. Such apparatus requires complex and costly equipment.
In other known methods, washing of the sand is carried out with compressed air, an air ejector disposed in the central portion of the filter allowing at the same time the recovery of the sand through a central tube and washing of the sand with air in such central tube, the sand being subjected to a washing operation with water at the upper portion of the filter.
Such methods have, however, disadvantages. The speed of passage of the sand in the central tube sometimes is too high, and air pockets form and do not participate in the washing of the sand. Moreover, abrasion hazards are high, as well as losses of sand by attrition. The consumption of compressed air is continuous. Moreover, the practicing of such methods requires a cylindrical apparatus of great height, provided with extra devices such as dispersion cones for the washed sand.